Generally, in an electrophotographic method utilized for image formation by a copying machine, a static charge is uniformly formed on the surface of a photoreceptor having a photoreceptive layer composed of a photoconductive material. Then a electrostatic image corresponding to the image to be formed is made on the surface of the photoreceptor by imagewise exposing to light. The electrostatic image is developed by a developer to form a toner image. The toner image is transferred to a recording medium such as paper and fixed.
Many characteristics are required to the developer to be used for the electrophotographic method. For example, a coloring ability, suitable electrostatic, thermal, mechanical and chemical properties, a suitable fluidity, an anti-blocking property and a powder property relating to the particle size distribution are required to the toner in the developer. The toner is comprised of a binder resin and a complex fine particle which is composed of a colorant and various materials for satisfying such the requirements.
When the image forming operation are repeatedly performed using such the developer, it is often observed that a charge providing member such as a carrier and a blade for forming a thin layer of developer was contaminated by a part of the materials constituting the toner, with the result that the static property of the toner is changed and a bad influence is occurred on the image quality. However, the material contaminating the charge providing member is various since the toner is constituted with various kinds of material. Accordingly, any simple relation cannot be found between the amount of the contaminating material and the variation of the charging property. As a result of that, effective countermeasure cannot be taken in the present condition.